The invention relates to a cathode ray tube comprising an electron gun for generating at least one electron beam, and a deflection unit for deflecting the at least one electron beam across a display screen, the deflection unit comprising a line deflection coil system and a frame deflection coil system, the line deflection coil system and/or the frame deflection coil system having coils which are at least partly provided with a conductive layer. The invention also relates to a deflection coil system.
WO 99/66526 (Attorney""s docket PHN 16960) describes a cathode ray tube (CRT) having line and frame deflection coil systems which are at least partly provided with a conductive layer. Such a layer reduces the occurrence of unwanted high-frequency electromagnetic oscillations between the line and the frame coil systems, which oscillations are known as the xe2x80x9cringingxe2x80x9d phenomenon. This phenomenon becomes visible in a gradually decaying curtain of lighter and darker vertical bars at the left-hand side of the screen.
The document discloses various ways of applying the conductive layer to the coil systems. In a first way, a conductive material layer is provided in one of the outer layers, e.g. the bonding layer of the wire used for winding the coils. During formation of the coils, the adhesive layers melt together and a conductive layer is formed in and on the coils. An alternative method of application is impregnating the coils with a solution of a conductive material and, subsequently, allowing the solution to dry. Thereafter, coil parts that should remain uncovered have to be cleaned. The use of PEDOT, ITO or ATO solutions is preferred.
The described ways of providing the coils with a conductive layer have their drawbacks. The first method has the drawback that wires having a conductive layer are more expensive. Furthermore, the adhesive and the winding characteristics of said wire are inferior to those of conventional wires. The second method requires additional process steps in the manufacture of the coils for a CRT. These additional process steps increase the cost price of the CRT.
It is an object of the invention to provide a cathode ray tube in which the indicated drawbacks are substantially reduced in a very simple and practical manner, without substantially impairing the required damping characteristics. To this end, the invention is characterized in that the coils comprise a composition of first electrically conductive wires having an electrically non-conductive layer surrounding the first electrically conductive wires and second electrically conductive wires having an electrically conductive layer surrounding the second electrically conductive wires. Coils provided with a conductive coating in this way have the surprising advantage that the indicated problems are reduced, while the required damping characteristics with respect to the unwanted high-frequency oscillations remain substantially the same as in the prior-art solutions where all wires have an electrically conductive layer.
Advantageous embodiments of the invention are described in the dependent claims.
These and other aspects of the invention will be elucidated with reference to the embodiments described hereinafter.